A very high output is required for a power amplifying apparatus to be used in a mobile base station or a transmitter for broadcasting. For example, one output reaches 40 to 80 W in a base station for WCDMA and reaches several kW in equipment for digital broadcasting. In such a transmitter, one power amplifier device cannot cover a single amplifier unit. For this reason, it is necessary to connect several devices or amplifier units in parallel.
FIG. 5 is a diagram showing the schematic structure of a power amplifying apparatus using a power combining system. As shown in FIG. 5, an input signal is distributed to a plurality of systems (parallel devices) by a distributor 101, and the signals thus distributed are amplified by power amplifiers 102a to 102c in the parallel units (devices) respectively and a signal synthesized by a synthesizer 103 is output. In such a conventional power combining system, it is necessary to accurately control the group delay of each parallel unit or device. For the most basic method for carrying out the group delay, a delay line is used in each parallel unit.
However, it is very hard to manufacture and regulate a parallel power combining system using the delay line in order to match the delays of the parallel units. In the case in which the regulation is not sufficient, a synthetic output power is attenuated or a frequency characteristic is generated on an output.
If an analog signal is input, moreover, it is possible to carry out a group delay measurement for a delay between an input and an output by using a network analyzer and to theoretically obtain the length of the delay line from a measured value (delay amount).
In an amplifier using such a parallel power combining system, however, an input is digital in a system using a digital predistortion (for example, JP-A-2003-332853), an EER (Envelope Elimination and Restoration) and an LINC (Linear amplification with Non-linear Components). Therefore, it is also impossible to carry out a group delay measurement using such as the network analyzer.